The present invention relates to valve systems that provide vacuum breaker or air release action or a combination of the two, and more particularly concerns such a valve system having improved response of the float in the presence of high velocity flow of liquid into the float chamber, and in which sensitivity of the pressure release valve to small variations of ball float position is decreased.
Valve systems are employed in pipelines to handle a number of conditions including air release, air pocket accumulation and lowered internal pressure. These conditions may arise during operations referred to in the following discussion.
Pipelines having varying elevations include high points of the line at which air collects either when the pipe is initially filled or over a period of time during operation of the pipe. For example, when a pipeline for flowing water is initially filled, air in the pipe must be released at the several high points in order to eliminate air pockets that may obstruct water flow. Further, after the pipe has been in operation for a period of time, bubbles of air in the water tend to collect at high points, displacing water from the pipeline at such points, and accumulating to an extent that will impede or block the water flow. Such air pockets may be under considerable pressure, which is equal to the pressure of the system liquid, and for release of such air a relief valve must be operable against or in the presence of this accumulated pressurized air. Under other conditions, such as, for example, when flow through a pipeline is shut off, pressure in the line may decrease, causing a negative pressure which can reach values that may cause collapse of the pipe. Thus it is common to install in a water pipline, for example, valves which permit release of undesired high pressure, permit release of air when the line is being filled, and admit ambient air when line pressure decreases.
Combined vacuum breaker and air release valves that are presently employed incorporate a relatively large area vacuum breaker valve and a relatively small area air release valve. When the system is empty, both valves of such a combination system are open with movable valve members being in a lower position from which they are movable upwardly to close the various orifices. As the system is filled, water rushes into the valve chamber, flowing around a float, which is generally a sphere, until the float rises to a point at which the valves are driven upwardly to closed position. It is found that in some circumstances when water flows into the float chamber of a valve of this kind, the ball float does not immediately rise in response to buoyant forces exerted by the increasing level of the water. On the contrary, in many situations, depending upon velocity of the incoming water, the ball will initially remain in a lower position in the float chamber and, only after water level in the chamber has risen to a significant extent, the ball will suddenly rise at high speed and cause the valve members to slam shut. This rapid and abrupt closing of the valves is undesirable, tending to be destructive of the system, as it may create excess stress and forces on the valve members and pipe.
In normal operation of a pipe system with an air release valve controlled by a ball float, liquid in the pipeline adjacent to the valve is occasionally subject to turbulence. In many conditions, particularly where the ball float chamber is only partly filled with water so that the ball is floating at an intermediate position, turbulent flow of water in the adjacent pipe is transmitted to the water within the chamber. The water in the chamber then experiences a relatively rapid fluctuation in level. As the water level moves up and down rapidly due to the disturbed flow, the float also moves up and down, experiencing small vertical perturbations. If the air release valve is seated, this vertical perturbation or bouncing of the ball float causes the valve member to oscillate rapidly through a small distance between open and closed positions and may cause water to be expelled from the valve, thus producing what is effectively a turbulence induced leakage.
Accordingly, it is an object of the present invention to provide a valve system that avoids or minimizes above mentioned problems.